Bulk magnetic properties of Co-Zn ferrites prepared by the co-precipitation method

The alternating current (a.c.) susceptibility versus temperature and magnetization measurements are reported for the disordered spinel ferrite system Zn _x Co_1-x Fe₂ O₄ prepared by a wet chemical method before and after high temperature annealing. The low field a.c. susceptibility measurements indicate that the low temperature synthesis of wet prepared Co-Zn ferrites aids the formation of spin-clusters and thereby increases the magnetic inhomogeneity. The X-ray analysis shows that the samples are single phase spinels and the variation of lattice constant with zinc concentration deviates from Vegard's law [1]. The high temperature annealing changes the wet prepared ferrites into the ordered magnetic structure of the ceramic ferrites.     

Microwave hydrothermal synthesis of nanosize PbO added Mg-Cu-Zn ferrites

Lead oxide added Mg-Cu-Zn ferrite powders were prepared by a co-precipitation method in a microwave-hydrothermal (M-H) system. The synthesized ferrite samples were characterized by powder X-ray diffraction (XRD), Infrared spectroscopy (IR), transmission electron microscopy (TEM) and Differential scanning calorimeter (DSC). Nanophase ferrites (~10–20 nm) with high surface area were synthesized at a low temperature of 160°C after a treatment time of 1 hour. The nano-powder was sintered at 900°C/4h in air atmosphere. The variations of the sintered density, electrical resistivity, initial permeability, and saturation magnetization with additive concentration have been investigated and the obtained results were compared with one prepared by the conventional ceramic method. It is found that the addition of PbO improves sintered density, electrical resistivity and permeability.     

Microwave hydrothermal synthesis of nanosize Ta2O5 added Mg-Cu-Zn ferrites

Tantalum oxide added MgCuZn ferrite powders were synthesized by a co-precipitation method using NaOH in a microwave-hydrothermal (M-H) apparatus. The phase identification of the prepared samples was done by X-ray diffraction and crystal size and morphology were determined by transmission electron microscopy (TEM). Nano-phase ferrites with high surface area were synthesized at 160°C after a treatment time of 1 hour. The M-H synthesized powders were conventionally sintered at a temperature of 900°C/4h. The variations of the sintered density, initial permeability and electrical resistivity as a function of additive concentration at room temperature have been investigated.     

An insight into the nanosize and bulk Ni0.5Co0.5Fe2O4 ferrites through their comparative study: Structural and magnetic investigations

Journal of Materials Science: Materials in Electronics - The proposed research work manifests the comparison of nanosized ‘as prepared’ Ni0.5Co0.5Fe2O4 ferrite with their...     

Peculiarities of photoluminescence of Al2O3 bulk and nanosize powders at low temperatures

Photoluminescence has been studied in the aluminum oxide (Al₂O₃) bulk and nanosize powders in the 300-8 K temperature range. In both samples luminescence spectrum is characterized by presence of broad blue and red bands caused mainly by emission from the uncontrolled titanium impurity. At low temperatures luminescence intensity increases by several times and the red band obtains fine structure. The nature of the fine structure is discussed suggesting manifestation of splitting of the Ti³⁺ emitting level due to Jahn-Teller effect or overlapping of Ti³⁺ emission band with narrow lines from other emitting ions. The observed differences in low-temperature spectral features of nanopowder compared to its bulk counterpart are explained by lattice structure of nanopowder, which belongs to transition phase of Al₂O₃.     

钴锌合金在氯化胆碱-尿素离子液体中的电沉积行为

为探索新型的Co-Zn合金电镀工艺,在氯化胆碱-尿素离子液体中电沉积了钴锌合金镀层,探讨了阴极电位、Co(Ⅱ)/Zn(Ⅱ)浓度比、温度及时间等工艺参数对电沉积的影响,并对合金镀层性能进行了测试.结果表明:在氯化胆碱-尿素离子液体中,控制体系的组成和沉积条件,可得到表面均匀、附着力强、有金属光泽的非晶态Co-Zn合金镀层,其中Co的质量分数可达90%.     

纳米银粒子的制备及其表征

采用聚乙烯吡咯烷酮、无水乙醇和去离子水混合溶液,利用水合肼还原硝酸银制备纳米银粒子.利用透射电子显微镜,紫外-可见吸收光谱和X射线衍射对纳米银粒子进行表征.结果表明,该法制备的纳米银粒子杂质含量低,粒度分布集中,颗粒均匀一致,形貌呈球形.     

Studies on BaO particles in nanosize regime

Barium oxide nanosize particles were prepared using the wet chemical route. Various capping agents were used to arrest the growth. X-ray diffraction studies reveal particle size as low as 9 Å in diameter, which is close to the Bohr exciton radius of BaO. However, changes in the optical absorption features arising from the confinement effect in the nanosize regime were not observed. These results were confirmed by fluorescence measurements. The calculations based on effective mass approximations indicate that the quantum confinement effects are not significant for particle sizes as small as 15 Å.     

尖晶石型纳米晶钴锌铁氧体的制备及其电磁和微波吸收性能

采用聚丙烯酰胺凝胶法制备了尖晶石型纳米晶CoxZn1-xFe2O4（x=0．2、0．5和0．8）．采用X射线、透射电镜、傅里叶红外光谱（FT-IR）和波导法对产物进行了表征．结果表明,纳米晶CoxZn1-xFe2O4的红外吸收峰、晶格常数和电磁性能依赖于Co^2＋含量．当CoxZn1-xFe2O4的x分别为0．2、0．5和0．8时,FT-IR显示铁-氧离子（Fe-O）键的特征吸收峰分别为561cm^-1、579cm^-1和584cm^-1．通过X射线衍射数据的计算得出,晶粒平均粒径分别为30．9nm、28．5nm和34．5nm;随着Co^2＋含量的增加,纳米晶CoxZn1-xFe2O4的晶格常数从0．8474nm减小到0．8409nm．在测试频率范围内,纳米晶CoxZn1-xFe2O4的介电损耗、磁损耗和反射率明显增大．     

Liquid phase epitaxy of hexagonal ferrites and spinel ferrites on non-magnetic spinel substrates

Using a PbOBaOB₂O₃ fluxed melt which had been employed previously to grow hexagonal ferrite Zn₂Y films on hexagonal ferrite M substrates, isothermal dipping liquid phase epitaxy produced epitaxial films on non-magnetic spinel substrates. The substrates studied were single crystals of three different compositions: MgAl₂O₄, MgGa₂O₄ and Mg(In,Ga)₂O₄. Two different film phases were identified: a lightly Zn-substituted M-type hexagonal ferrite and a heavily Zn-substituted magnetite.     

Synthesis of nanosize mesoporous MCM-48 material

Nanosize mesoporous material MCM-48 was synthesized under the hydro-thermal system. The results of TEM and SEM show that the obtained MCM-48 is well organized on a 100 A length scale. Both the Nanosize and the superior organization provide this material with good thermal stability.     

Local and global instabilities in nanosize rectangular prismatic gold specimens

We use molecular mechanics simulations with the tight-binding potential to study local and global instabilities in initially defect-free nanosize rectangular prismatic specimens of gold deformed in tension/compression and simple tension/compression. Whereas in simple tension/compression atoms on end faces are constrained to move axially but are free to move laterally and the cross-sectional dimensions of end faces can change, in tension/compression all three components of displacements of atoms on end faces are prescribed and the cross-section of an end face does not change. The three criteria used to delineate local instabilities in a specimen are: (i) a component of second-order spatial partial derivatives of the displacement field has large value relative to its average value in the body, (ii) the minimum eigenvalue of the Hessian of the potential energy of an atom is negative, (iii) a relatively high value of the common neighborhood parameter. A specimen becomes globally unstable when its potential energy decreases noticeably with a small increase in its deformations. It is found that the three criteria for local instability are met essentially simultaneously at the same atomic position. Deformations of interior points of a specimen are different when it is deformed in simple tension/compression from those in tension/compression. It is found that the initial unloaded configuration (or the reference configuration) of the minimum potential energy has significant in-plane stresses on the bounding surfaces and non-zero normal stresses at interior points. This initial stress distribution satisfies Cauchy’s equilibrium equations for a continuum. In deformations of a nanobar studied here, the yield stress defined as the average axial stress when the average axial stress vs. the average axial strain curve exhibits a sharp discontinuity depends upon the specimen size. It is shown possibly for the first time that deformations of the specimen are reversible if it is unloaded prior to yielding but have a permanent strain if unloaded after it has yielded. Because of residual stresses in the reference configuration, the average axial stress at yield in compression is nearly one-half of that in tension. The slope of the average axial stress vs. the average axial strain curve during unloading after it has yielded is the same as that during initial loading up to the yield point.     

Infrared absorption in spinel ferrites

Their spectra of a number of ferrites, MFe₂O₄, M(Mn, Fe, Co, Ni, Cu and Zn) have been studied at room temperature in the range 200–1000 cm⁻¹. In all the cases the spectrum consists of four bands, two of which have strong absorption while the other two have weak absorption and often appear as shoulders on the main band. However up to 20% of the inverse ferrite, the shoulder in the low energy side appears as a band. In this paper we have analysed the origin of the above bands.     

Neutron investigation of ferrites

This article reviews the work carried out at Trombay in a variety of single and mixed spinel ferrites. The use of polarised neutrons in the elucidation of cation distribution and magnetic structures in powder specimens is emphasised. Magnetic form factor studies in single crystal specimens of Fe₃O₄ and MnFe₂O₄ are described. Evaluation of dominant exchange interactions in a few powder specimens in their paramagnetic phase using the cold neutron scattering technique is described. Measurements of the acoustic magnon dispersion in MnFe₂O₄ and Li_0.13Fe_2.87O₄ are outlined.     

Electrical conductivity of zinc ferrites near stoichiometry and manganese-zinc ferrites under vacuum or in the presence of oxygen

The electrical conductivity of zinc ferrites near stoichiometry and of manganese-zinc ferrites has been investigated as a function of temperature under vacuum and in the presence of oxygen. Under vacuum, the conductivity of these ferrites with iron excess is explained by the hopping mechanism, and with ZnO excess by the development of vacancies in octahedral sites of cation-deficient spinel. Activation energies and the transition temperatures are presented. During the oxidation in oxygen of Mn-Zn ferrites, the profile of the log σ= f(T) curves shows that the mechanism of electrical conduction in the temperature range 100 to 350 °C can be explained in terms of the oxidation of Fe²⁺ to Fe³⁺ ions at octahedral sites. For the temperature range 300 to 450 °C, the conductivity involves the hopping of electrons from octahedral sites of Mn³⁺ ions to octahedral sites of Mn⁴⁺ ions. Above 550 °C the oxidation of Mn²⁺ ions leads to a marked change in conductivity with the generation of new phases.     

Plasma spraying of ferrites

The production of thick films (> 20 m) of polycrystalline ferrite by the arc plasma deposition process is described. Operating conditions of a plasma torch of the authors' own design are quoted. As-sprayed films have high electrical conductivity and low magnetic permeability, but these parameters are restored close to the bulk values by annealing. The surface finish of the films is coarse and unaffected by the particle size of the powder sprayed.